Chemical sensors are generally known for use in a wide variety of areas such as medicine, scientific research, industrial applications and the like. Fiber optic and electrochemical approaches are generally known for use in situations where it is desired to detect and/or measure the concentration of a parameter at a remote location without requiring electrical communication with the remote location. Structures, properties, functions and operational details of fiber optic chemical sensors can be found in U.S. Pat. No. 4,577,109 to Hirschfeld, U.S. Pat. No. 4,785,814 to Kane, and U.S. Pat. No. 4,842,783 to Blaylock, as well as Seitz, "Chemical Sensors Based on Fiber Optics," Analytical Chemistry, Vol. 56, No. 1, January 1984, each of which is incorporated by reference herein.
Publications such as these generally illustrate that is it known to incorporate a chemical sensor into a fiber optic waveguide, an electrochemical gas sensor or the like, in a manner such that the chemical sensor will interact with the analyte. This interaction results in a change in optical properties, which change is probed and detected through the fiber optic waveguide or the like. These optical properties of chemical sensor compositions typically involve changes in colors or in color intensities. In these types of systems, it is possible to detect particularly minute changes in the parameter or parameters being monitored in order to thereby provide especially sensitive remote monitoring capabilities. Chemical sensor compositions that are incorporated at the distal end of fiber optic sensors are often configured as membranes that are secured at the distal tip end of the waveguide device or optrode.
Gas sensors of this general type are useful in monitoring gas concentrations such as oxygen and carbon dioxide in bloodstreams and the like. Also, it is sometimes desirable to provide sensors that monitor other parameters such as pH. Ion concentrations can also be detected, such as potassium, sodium, calcium and metal ions.
A typical gas-sensor device positions the sensor material at a generally distal location with the assistance of various different support means. Support means must be such as to permit interaction between the gas indicator and the substance being subjected to monitoring, measurement and/or detection. Known approaches in this regard include the use of permeable membranes and composites incorporating micro-encapsulation. With certain arrangements, it is desirable to incorporate membrane components into these types of devices. These membrane components must possess certain properties in order to be particularly advantageous. Many membrane materials have some advantageous properties but also have shortcomings. Generally speaking, the materials must be biocompatible, they must be permeable to the gas being monitored, and they must be capable of supporting the gas-sensitive indicator, while at the same time possessing the strength adequate to permit maneuvering of the device without concern about damage to the gas sensor. It is also desirable to have these materials be photocurable in order to facilitate locating the gas sensor composite on the device.
In summary, the present invention is addressed to novel polymer compositions which have been found to be particularly suitable for use as membranes and membrane-like components which incorporate gas-sensitive indicators to form the active gas sensor component of a gas sensor device. The polymer compositions are particularly useful in fiber optic sensors for measuring dissolved gases, particularly O.sub.2 or CO.sub.2, in a fluid. The polymer compositions are cured perfluorinated urethane polymers formed by cross-linking a perfluorinated urethane precursor using a suitable cross-linking agent. Relative to previously known and used gas sensors, the present polymer compositions provide for gas sensors of superior sensitivity, resolution, solvent resistance and photostability. In addition, gas sensors fabricated with the present polymer compositions display increased resistance to fluid flow and shear, because of increased adhesion of the polymer composition to the fiber substrate. Also, the polymer compositions described herein generally require a lower level of cross-linking agent, and will typically contain very little or no residual monomer after cure. Finally, the present polymer compositions have been found to increase the life of the gas sensor by eight- to ten-fold.